1. Field of Invention
This invention relates to cellular electrical stimulation in general, for animals, including humans, and neuronal and muscular electrical stimulation in particular, for brain, spinal cord, peripheral nerves, and muscles, as heart and artificial limbs.
2. Discussion of Prior Art
It is well established that the nerves work as a electrical conductor, neural information being simply electrical train of pulses—short burst of pulses repeated at short time intervals, potentially followed by a longer pause. Measurements on animals have shown that the brain works the same way, and in the few cases in which measurements have been made in humans, it has been confirmed that H. sapiens brain is also an electric machinery. The brain acts also as a network creator using synaptic generation and strengthening.
It follows that control of the electrical path of neurons in the brain, and flow of electrical current through its cells can potentially affect the brain activity, whether it be related to motor control, to emotion arousal or just a thought pattern. Among the clinical possibilities, mechanical failures has been the most successful so far, and among these, control of Parkinson's Disease is a case. Parkinson's Disease control is not the only one, some other similar motor control being very successful too, as epilepsy and essential tremor. Other cases are now under evaluation, as depression and eating disorders, to mention just two examples. Electrical stimulation is also used to control pain, as in TENS devices, to control incontinency and potentially any other neuronal malfunction. And naturally that electrical stimulators are also used to adjust the heart beating with the pacemaker, which is one of the oldest application of electrical stimulation.
As an exemplary case we will take the DBS (Deep Brain Stimulation) for Parkinson's Disease control, which is one of the most successful today, with several thousand surgeries performed yearly. The success rate is nevertheless less than what could be. Some of the failures are due to side effects, which may well be a consequence of incorrectly placed stimulators, as acknowledged by many neurosurgeons, including in this case stimulators placed other than the exact center of the target area. The reader should keep in mind that the word “area” in brain means what is normally called a volume; it happens that the neurons that participate together for a particular function are generally connected on a network that is mostly flat (2-D), with little depth (3rd dimension), which is the origin of the word usage. Ultimately this word usage is adopted even when a particular “area” happens to be actually volumetric (that is, having a non-negligible 3rd dimension). Indeed, it is very difficult for the neurosurgeon to place the stimulating electrode in the correct place, deep inside the brain and not even open to visual inspection. Current art, for example, the stimulating electrode manufactured by Medtronic (REF_Meditronic_nd) attempts to adjust the final stimulating position offering 4 ring-like stimulating elements, which are at the end of a wand, called “lead” by Medtronic (which we call picafina), each of which can be independently chosen as the stimulating element. The rings are approximately 1 mm in width and separated by 1 mm too. Consequently, after insertion of the picafina in the patient's brain, it is possible to chose the stimulating site with the picafina in the same position, just connecting one ring or another ring to the electrical pulse circuit, while disconnecting the others, or to choose two rings, or many other possible combinations of rings. This final stimulating positioning adjustment is made after the surgery, to compensate for the expected inaccuracies of initial position of the picafina with respect to the desired placement in the brain. Stimulating ring selection can be also needed to compensate for later possible motion of the picafina with respect to the brain. Unfortunately, the picafina must be of small size in order to minimize injure to the brain tissue, which in turn precludes many wirings running through it, this being one of the reasons for the current devices having so few stimulating pads (or rings, or electrodes) which offer so few options for the origin of the stimulating pulses. Indeed, many neurosurgeons would like to have more options, more electrical pads to choose as initiation points for the electrical stimulation, but a solution for this problem was never found. One possible solution is disclosed in patents applied by some of us (INV1, INV2, INV3, INV4, INV5), but alternative solutions exist too. Our invention offers an improvement on this positioning of the stimulating electrodes, and an improvement independent of our earlier inventions cited on this subject.
It is worth to point out that the prior art is capable of initiate an electrical stimulation from any of the four rings, therefore offering a small (1 mm.) adjustment on the stimulation site, but it is not capable of offering adjustment on the stimulation site from the position where one of the ring is to another site where the insulator spacer is. If the ideal position of the stimulator happens to be where one of the separators are, either one of the two adjacent rings have to be selected, of both of them, but no more precise than this. Neither can prior art cause the stimulation to be along one direction only, though the authors are aware of one lead manufactured by Medtronic which sports a small number of isolated pads, which are not circular around the lead but more-or-less rectangular on the surface of the lead.
A similar problem is encountered by heart pacemakers. A pacemaker have to deliver electrical pulses to some particular point in or near the heart. Typically the delivery point is nowadays in the inner wall of the heart, but this is not necessarily so, some pacemakers being attached to the external wall of the heart too. There are malfunctions that are better treated with a dual electrode, and more than two electrodes may become common in the future. Some of these electrodes are inserted via a vein accessed near the neck into the inner wall of the atrium, or upper heart chamber, where the delivering electrode is screwed in the inner wall of the atrium for spatial stability and consistency of electrical delivery point. In current art devices, the tip of the flexible device is made of some electrically conductive material, which is connected by wires to a battery/electronic circuits, which are located elsewhere in the patient, usually the upper chest. Old art has the disadvantage that the electrical pulse is injected over the whole, or at least most of the volume of the attachment. This has the disadvantage that the pulse is injected over too large an area into the heart muscle to be able to control its propagation time, which is needed for a proper, sequential contraction of the heart muscle, needed for optimal pumping. If the electrical pulse is not injected correctly, then the heart pumping is not sequentially squeezing the blood forward, as needed, causing a non-optimal pumping.
Regarding the position, it is not necessary to attach the electrode to the atrium, and our invention should not be limited to this case. In this case the pacemaking pulse is delivered symmetrically around the screw, 360 degrees around it, and it is delivered by all the metallic (or conductive) part of the tip of the device. Yet, such symmetrical delivery is not desirable, because the normal, natural electrical pulse is known to travel through the heart along certain paths with specific speeds and delay times, starting from the sinus, these speeds and delays being a function of the electrical characteristics of the heart muscle, known in electrical engineering as resistance, capacitance, inductance, etc. Normally the pulse initiates from a nerve that delivers it on the coronary sinus, and from there the electrical pulse propagates with speeds that depend on the tissue properties along each direction, which is a much studied problem. This point of delivery is a problem that has not yet been solved, in spite of it being a known source of problems with the pacemaking pulse. Indeed, if the electrical pulse from the pacemaker is delivered in the wrong place then the heart will not beat correctly, because the contraction, which must happen in a particular sequence will not be correct. A good example of the problem is the analogy with a milkman, who must start squeezing the teat near the udder, with his pointing finger (which is usually the one closer to the udder), then the middle finger, then the annular finger, then the small finger by last, if the milk is to be extracted from the utter through the teat. If he reverts the order, or change the other in any way, either no milk at all, or at most less milk will be squeezed from the caw. The pathways for the electrical pulses that originate at the sinus node are well known and it is well known that replication of the natural electrical pulse would be ideal, but an ideal that has eluded the devices in current use. Ideally the heart surgeon would be able to precisely control the depth on the heart wall and direction of delivery of the electrical pulse, as opposed of the voltage only, which is the only controllable value in current art, which also delivers the pulse on all directions, which is not ideal either.